1. Field of the Invention
The present invention relates to a method for manufacturing a plane light source, and more especially, to a method to enhance the luminous efficiency of the plane light source.
2. Background of the Related Art
Flat panel display (FPD) has received a great deal of attention. Very recently, the development of large area panel such as high definition television and high information content presentation becomes a major trend of the technical development in the FPD community. Enormous competition has being placed in the FPD industry where the traditional cathode-ray tube (CRT) has been largely challenged and replaced gradually by more brighter, thinner and purer luminous alternatives such as the thin film transistor-liquid crystal display (TFT-LCD), the field emission display (FED) and the plasma display panel (PDP), etc. Among those display models, it is the most critical to develop an efficient illuminating technology, i.e., the plane light source. Illuminating phosphors are of the concern since they provide an illuminating source with improved brightness, cost-effectiveness, stability, and uniformity compared to the currently-used cold cathode fluorescence lamp (CCFL). However, the phosphor presents a poorer efficiency of illumination than the latter. This will become a critical issue if a large-area display panel is to be targeted.
Efficiency, together with brightness and luminous purity, of the white light illumination is affected by a number of factors including the nature of phosphor materials, particle size, particle morphology, and packing efficiency of the phosphor powder upon screen printing. In addition, the illuminating behavior of the phosphor is essentially surface-luminescent upon a given excitation of such as the vacuum ultraviolet (VUV) irradiation. Therefore, the surface characteristics and morphology of the phosphor particles will play an important role in the resulting illumination property.
Currently, the plane light source has three kinds of phosphors: (Y,Gd)BO3:Eu (YGB, red color), BaMgAl10O17:Eu (BAM, blue color) and Zn2SiO4:Mn (ZSM, green color), wherein the blue color phosphor has the lowest luminance and the shortest lifetime comparing to the others, and it gets even worse after the panel manufacturing process is completed. U.S. Pat. No. 6,627,114 discloses a phosphor coated with Mg or P to optimize the luminescent materials for a plane light source, wherein the phosphors coated with Mg or P have smoother decay than those without coating. However, the initial brightness of the coated phosphors in initiating is less bright than those without coating.